1. Field of the Invention
The present invention relates to an inner focus lens system and an image pickup apparatus using the same.
2. Description of the Related Art
Conventionally, a so-called Gauss type wide-angle lens has been known as a wide-angle lens used for a photographic camera and a still video camera. A Gauss type lens system is a lens system in which a refractive power arrangement is substantially symmetric across an aperture stop. The Gauss type lens system includes lens systems described in Japanese Patent Application Laid-Open No. 2003-241084 and Japanese Patent Application Laid-Open No. 2009-258157. The lens systems described in Japanese Patent Application Laid-Open No. 2003-241084 and Japanese Patent Application Laid-Open No. 2009-258157 are wide-angle lenses at about F2.8.
Further, as a similar Gauss type lens system, there is a lens system described in Japanese Patent Application Laid-Open No. 2009-237542. The lens system described in Japanese Patent Application Laid-Open No. 2009-237542 is a large-diameter (about F1.8) standard lens. Further, as a lens system which has realized a further larger diameter (about F1.4), there is a lens system described in Japanese Patent Application Laid-Open No. 2010-66432.
In the Gauss type lens systems as described in the above publications of unexamined applications, a lens unit having a positive refractive power is located on an image side than an aperture stop, and the entire lens unit having this positive refractive power is brought up (moved toward an object side). Thus, the Gauss lens systems as described in the publications of unexamined applications are lens systems employing a so-called rear focus method.